The incidence of breast cancer in Korea is the fourth to fifth most common cancer among women in the 1990s, but most patients have been completely cured since 2001, and breast cancer is known to be the most severe cancer excluding thyroid cancer with a good prognosis. For example, according to age-standardized incidence rates of carcinomas in Korean female cancer patients, it can be confirmed that the incidence of breast cancer is most sharply increasing excluding thyroid cancer, the incidence of which is rapidly increasing due to the spread of diagnostic devices such as ultrasound. Therefore, there is a need to develop a method of accurately diagnosing and treating breast cancer.
Meanwhile, up to date, there are three main methods of treating cancer, which is a malignant tumor: invasive surgery, radiotherapy, and chemotherapy, and cancer is treated by one or a combination thereof. In particular, invasive surgery is a method of removing most of the diseased tissue, and such invasive surgery is inappropriate to treat tumors in sites that are difficult to remove or to treat disseminated tumors. In addition, radiotherapy is mainly used in acute inflammatory diseases, benign or malignant tumors, endocrine dysfunction, allergic diseases, and the like, and is generally effectively used for malignant tumors consisting of rapidly dividing cells. Such radiotherapy is disadvantageous in that radiotherapy may weaken or lose the function of normal tissues and may cause skin diseases in treated sites after the therapy, and, in particular, may cause severe side effects such as delayed intelligence development or bone developmental disorders in the case of children with developing organs. In addition, chemotherapy is widely used to treat breast cancer, lung cancer, and testicular cancer by disturbing the replication or metabolism of cancer cells, and such a method is most disadvantageous in that there are side effects induced by systemic chemotherapy used in cancer treatment. The side effects by chemotherapy may have a significant effect on patients' lives and increase patients' anxieties about treatment. In addition, a side effect associated with chemotherapeutic agents is dose limiting toxicity (DLT), which should be generally taken into account when administering these drugs. For example, mucositis is DLT for various anticancer drugs (5-fluorouracil and methotrexate, which are antimetabolite cytotoxic agents, and doxorubicin which is an antitumor antibiotic). Among these chemotherapy side effects, the most severe cases require hospitalization or painkillers for the treatment of pain. As such, side effects due to chemotherapy and radiotherapy have become an important issue in the treatment of cancer patients.
Thus, as an alternative to addressing the above-described problems of conventional cancer therapeutics, cancer-related gene targeting treatment has attracted much attention. In particular, breast cancer gene 1 (BRCA1), breast cancer gene 2 (BRCA2), and the like have been reported as genes associated with the onset of breast cancer, and research thereon has been actively conducted (see Korean Patent Application Publication No. 10-2013-0057760), but results thereof are insufficient.